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16 workers can complete a piece of work in 30 days. After working for 10 days, 4 more workers joined.
How many fewer days did the work take?
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(1) Since 16 men can do the job in 30 days, their rate of work is part of job per 1 man per day.
(2) After working for 10 hours, 16 men completed = of the job;
hence, 1 - = remained to complete.
(3) How many days will it take for 16+4 = 20 men to complete the remaining {{2/3}}} of the job ?
Divide the remaining job by = . You will get
remaining time = = = 2*8 = 16 days.
ANSWER. 16 days after 4 men joined.
Or, which is the same, 4 days fewer, comparing with the original schedule.
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When I see such question "How many fewer days did the work take?", I always ask myself "how many fewer . . . comparing with WHAT ?".
In this form, "How many fewer days did the work take?", the question is UNCOMPLETED (!)